Attenuator with switch function and mobile telephone terminal device using the same

ABSTRACT

A high frequency part, which amplifies a high frequency signal outputted from an intermediate frequency part and supplies to an antenna, is equipped with a gain controller with switch function. The gain controller with switch function comprises an attenuator with switch function has a function of switching a selected band between two bands outputted from the intermediate frequency part and controlling the gain of the high frequency signal in the selected band. The attenuator with switch function comprises a first variable resistor which connects a signal input part with a signal output part and a second variable resistor which is disposed parallel to said first variable resistor and connects a signal input part with a signal output part. The first and the second variable resistors are controlled by a common gain control voltage and set such that the gain control voltage ranges, which are for changing the resistor values, will not overlap with each other.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a dual-band (mode) mobile telephoneterminal device, and more particularly, to the structures of anattenuator and a switch of a high frequency part disposed inside a radiopart of such a mobile telephone terminal device.

2. Description of the Related Art

A digital method (such as PDC) requires that the intensity of anelectric wave received by a base station from a mobile telephoneterminal device remains constant regardless of a change of a distancebetween the mobile telephone terminal device and the base station.Hence, a sender part of the mobile telephone terminal device performsgain control.

FIG. 9 schematically shows a positional relationship between a basestation and a mobile telephone terminal device. In FIG. 9, one basestation BS has a cell range CL which is at a radius of dozens ofkilometers, e.g., about 30 km. Within the cell range CL of this basestation BS, there are more than one mobile telephone terminal devicesTH₁ and TH₂ which are not at the same distance from the base station BSor which are not under the same telecommunications conditions such asgeography. These more than one mobile telephone terminal devices TH₁ andTH₂, while constantly changing their distances from the base station BSor the telecommunications conditions, simultaneously communicate withthe base station BS.

In such a situation, considering the size of the cell range CL, the gaincontrol width in the sender part of the mobile telephone terminal devicemust be about 50 dB or more so that the intensity of an electric wavereceived by the base station from the mobile telephone terminal devicewill be the same between the closest place to the base station BS andthe farthest place from the base station BS within the cell range CL ofthe base station BS. This is known as the near-far problem.

If the sender part of the mobile telephone terminal device fails toachieve excellent gain control, the intensity of an electric wavereaching the base station will mount as the distance between the mobiletelephone terminal device and the base station decreases. This willincrease leakage power to a neighboring channel. As a result, thedigital error rate will grow and the speech quality will deteriorate.

FIG. 10 shows the intensities of receive signals on the respectivechannels within the base station and an inter-modulation distortioncharacteristic. In FIG. 10, the solid lines A₁ through A₆ denote theintensities of electric waves received by the base station on therespective channels and the broken line B₄ denotes the inter-modulationdistortion characteristic on the channel A₄. From FIG. 10, it is seenthat the intensities of electric waves received on the channels A₃ andA₅ are dominated by a distortion component on the channel A₄ which isdenoted at the broken line B₄ and correct data therefore cannot berestored from the channels A₃ and A₅ which are adjacent to the channelA₄.

The sender part of the mobile telephone terminal device preferablyperforms gain control at its high frequency part, at which the level ofa carrier signal is high, as much as possible in order to maintain astate that a ratio (C/N) of the carrier signal level to the noise levelis high. This is because the level of the carrier signal is far higherthan the level of a background noise at the high frequency part, andtherefore, even when the gain is lowered at the high frequency part, thestate that the carrier signal is far different from the noise level ismaintained.

On the contrary, since the level of the carrier signal is low at anintermediate frequency part, when the gain is lowered at theintermediate frequency part, the difference between the level of thecarrier signal and the level of a background noise becomes marginal andthus shrank difference between the carrier signal level and thebackground noise level will hence be directly passed on to the highfrequency part.

For the purpose of gain control over the range of 50 dB or higher,within the sender part of the radio part of the mobile telephoneterminal device, the high frequency part controls the gain stepwise andthe intermediate frequency part controls the gain continuously. The useof both the gain control at the high frequency part and the gain controlat the intermediate frequency part realizes gain control over the rangeof 50 dB or higher.

Gain control in a mobile telephone terminal device is performed in thefollowing manner. That is, based on the intensity of a receive signalreceived by the mobile telephone terminal device, the mobile telephoneterminal device sets a target value for sending power which is needed tomaintain the intensity of the receive signal at the base stationconstant. The target value is compared with the actual sending power, afeedback control loop which makes the sending power follow the targetvalue is built, and gain control is executed so that the sending powerwill be the same as the target value.

FIG. 11 shows a base station BS(A) using a band A (mode A) and its cellrange CL(A) and a base station BS(B) using a band B (mode B) and itscell range CL(B). Also illustrated in FIG. 11 are mobile telephoneterminal devices TH₀, TH₁, TH₂, TH₃ and TH₄ which are under differenttelecommunications conditions, that is, which are at different distancesfrom the mobile telephone terminal device TH₁.

A dual-band (mode) mobile telephone terminal device, as shown in FIG.11, switches between the bands (modes) when moving out from the cellrange CL(A) of the base station BS(A) to the cell range CL(B) of thebase station BS(B). The bands A and B indicate that the terminal deviceuses different frequency bands, while the modes A and B indicate thatthe terminal device uses different systems.

While gain control used to ensure that the intensities of electric wavesreceived by the base station BS(A) from the mobile telephone terminaldevices TH₀, TH₁ and TH₂ would be the same within the cell CL(A),instantly upon entry into the cell CL(B), the mobile telephone terminaldevices TH₀, TH₃ and TH₄ switch the band (mode) and gain control thenensures that the intensities of electric waves reaching the base stationBS(B) would be the same.

The structure and operations of a conventional mobile telephone terminaldevice will now be described with reference to FIG. 12. This mobiletelephone terminal device, as shown in FIG. 12, is comprised of abaseband part 100 which is formed by a microcomputer logic part or thelike and processes a speech signal and a radio part 200 which receivesthe speech signal processed by the baseband part 100 and communicateswith a base station.

The radio part 200 comprises a sender part 210 which generates a sendsignal to the base station and a receiver part 220 which receives thesend signal from the base station.

The sender part 210 comprises an intermediate frequency part 230, aband-A high frequency part 240 and a band-B high frequency part 250. Theintermediate frequency part 230 modulates a speech signal fed from thebaseband part 100, adjusts the gain of an intermediate frequency signaland performs mixing for frequency conversion. The high frequency parts240 and 250 each amplify high frequency signals outputted from theintermediate frequency part 230 and supply to an antenna 300 via aswitch 310.

The intermediate frequency part 230 is comprised of a modulator 231which modulates an intermediate frequency signal in accordance with thespeech signal fed from the baseband part 100, a variable gainintermediate frequency amplifier 232 which amplifies, using a variablegain, the intermediate frequency signal which is an output signal fromthe modulator 231, and a mixer 233 which is for converting an outputsignal from the variable gain intermediate frequency amplifier 232 intoa high frequency.

The variable gain intermediate frequency amplifier 232 described aboveis formed by a bipolar transistor in many instances. The variable gainintermediate frequency amplifier 232 is capable of varying the gain overthe range of about 30 dB at the linearity of ±1 dB. In this case, thegain is continuously controlled over the range of about 30 dB, by meansof a gain control voltage which changes continuously.

The high frequency part 240 is comprised of a variable gain highfrequency amplifier 241 which amplifies, using a variable gain, theband-A high frequency signal outputted from the intermediate frequencypart 230, a power amplifier 242 which power-amplifies an output from thevariable gain high frequency amplifier 241 and a switch 245 which is forselecting the band A. The variable gain high frequency amplifier 241described above is capable of varying the gain over the range of about20 dB at the linearity of ±1 dB. In this case, the gain is continuouslycontrolled over the range of about 20 dB, by means of a gain controlvoltage which changes continuously.

The variable gain high frequency amplifier 241 is comprised of apreamplifier (intermediate power amplifier) 243 and an attenuator 244which is cascaded with the preamplifier 243 and varies the gain of theband-A high frequency signal which is supplied to the power amplifier(high power amplifier) 242. The attenuator 244 is equipped with afunction of changing the attenuation over the range of about 20 dB atthe linearity of ±1 dB.

The high frequency part 250 is comprised of a variable gain highfrequency amplifier 251 which amplifies, using a variable gain, theband-B high frequency signal outputted from the intermediate frequencypart 230, a power amplifier 252 which power-amplifies an output from thevariable gain high frequency amplifier 251 and a switch 255 which is forselecting the band B. The variable gain high frequency amplifier 251described above is capable of varying the gain over the range of about20 dB at the linearity of ±1 dB. In this case, the gain is continuouslycontrolled over the range of about 20 dB, by means of a gain controlvoltage which changes continuously.

The variable gain high frequency amplifier 251 is comprised of apreamplifier (intermediate power amplifier) 253 and an attenuator 254which is cascaded with the preamplifier 253 and varies the gain of theband-B high frequency signal which is supplied to the power amplifier(high power amplifier) 252. The attenuator 254 is equipped with afunction of changing the attenuation over the range of about 20 dB atthe linearity of ±1 dB.

The baseband part 100 includes a control part 110. The control part 110judges the band for the high frequency signal to be sent based on thereceive signal received at the receiver part 220 and adds a switchvoltage V_(SW)(A) to the switch 245 while adding a switch voltageV_(SW)(B) to the switch 255, thereby selecting the band for the highfrequency signal to be sent.

During a telecommunication in the frequency band of the band A, thecontrol part 110 detects the signal intensity of the receive signalreceived at the receiver part 220, detects the output level of the poweramplifier 242, and sets a target value for the output level of the poweramplifier 242 in accordance with the signal intensity of the receivesignal. The output level of the power amplifier 242 is compared with thetarget value for the output level of the power amplifier 242, a gaincontrol voltage V_(C)(A) corresponding to the comparison result is addedto the attenuator 244, and a gain control voltage V_(C)(C) correspondingto the comparison result is similarly added to the variable gainintermediate frequency amplifier 232. In this manner, the gain at theattenuator 244 and the gain at the variable gain intermediate frequencyamplifier 232 are follow-up controlled so that the output level of thepower amplifier 242 will coincide with the target value for the outputlevel of the power amplifier 242.

Meanwhile, during a telecommunication in the frequency band of the bandB, the control part 110 detects the signal intensity of the receivesignal reaching the receiver part 220, detects the output level of thepower amplifier 252, and sets a target value for the output level of thepower amplifier 252 in accordance with the signal intensity of thereceive signal. The output level of the power amplifier 252 is comparedwith the target value for the output level of the power amplifier 252, again control voltage V_(C)(B) corresponding to the comparison result isadded to the attenuator 254, and a gain control voltage V_(C)(C)corresponding to the comparison result is similarly added to thevariable gain intermediate frequency amplifier 232. In this manner, thegain at the attenuator 254 and the gain at the variable gainintermediate frequency amplifier 232 are follow-up controlled so thatthe output level of the power amplifier 252 will coincide with thetarget value for the output level of the power amplifier 252.

Utilizing both gain control at the variable gain high frequencyamplifier 241 or the variable gain high frequency amplifier 251 and gaincontrol at the variable gain intermediate frequency amplifier 232, themobile telephone terminal device described above realizes gain controlover the range of 50 dB or higher.

In accordance with the PDC standard, an input stage of the mixer 233operates in the 200 MHz band while an output stage of the mixer 233operates in the 940 or 1441 MHz band. As for the signal levels at therespective parts in such a state that the mobile telephone terminaldevice yields the maximum output, the signal level at an output terminalof the power amplifier 242 or the power amplifier 252 is +30 dBm (where0 dBm=1 mW), the signal level at an output terminal of the variable gainhigh frequency amplifier 241 or the variable gain high frequencyamplifier 251 is +8 dBm, the signal level at an output terminal of theswitch 245 or the switch 255 is −16 dBm, the signal level at an outputterminal of the mixer 233 is −15 dBm, and the signal level at an outputterminal of the variable gain intermediate frequency amplifier 232 is−20 dBm.

When the variable gain high frequency amplifier 241 controls the gainover the range of 20 dB and the variable gain intermediate frequencyamplifier 232 controls the gain over the range of 30 dB, the signallevel at the output terminal of the variable gain intermediate frequencyamplifier 232 changes in the range of −20 dBm through −50 dBm.Meanwhile, the signal level at the output terminal of the mixer 233changes in the range of −15 dBm through −45 dBm. The signal level at theoutput terminal of the switch 245 or the switch 255 changes in the rangeof −16 dBm through −46 dBm. The signal level at the output terminal ofthe variable gain high frequency amplifier 241 or the variable gain highfrequency amplifier 251 changes in the range of +8 dBm through −42 dBm.The signal level at the output terminal of the power amplifier 242 orthe power amplifier 252 changes in the range of +30 dBm through −20 dBm.

The specific structures of the attenuator 244 (254) and the switch 245(255) and their operations at the time of switching of the band will nowbe described with reference to FIGS. 13 through 15.

FIG. 13 is a circuit diagram which shows the structure of the attenuator244 (254). Such an attenuator 244 (254) controls the gain. Theattenuator 244 (254) is comprised of a resistor 2 (12) and a fieldeffective transistor 1 (11) which serves as a series variable resistor,as shown in FIG. 13.

Disposed to the attenuator 244 (254) are a gain control voltage applyingterminal 5 (15) which is for applying a gain control voltage V_(C), asource voltage applying terminal 6 (16) for applying a power sourcevoltage V_(DD), an input terminal 3 (13) which serves as a signal inputpart IN for the high frequency signal, and an output terminal 4 (14)which serves as a signal output part OUT for the high frequency signal.

The input terminal 3 described above is connected with the outputterminal of the switch 245, while the output terminal 4 is connectedwith an input terminal of the preamplifier 243. The resistor 2 plays arole of blocking leakage of the high frequency signal. Meanwhile, theinput terminal 13 is connected with the output terminal of the switch255 which is shown in FIG. 12, and the output terminal 14 is connectedwith an input terminal of the preamplifier 253. The resistor 12 plays arole of blocking leakage of the high frequency signal.

FIG. 14 is a circuit diagram which shows the structure of the switch 245(255). Such a switch 245 (255) switches the band. The switch 245 (255)is formed by a resistor 22 (32) and a field effective transistor 21 (31)which serves as a series variable resistor, as shown in FIG. 14.

Disposed to the switch 245 (255) are a switch voltage applying terminal26 (36) which is for applying a switch voltage V_(SW)(A) (V_(SW)(B)), agate voltage applying terminal 25 (35) which is for applying a groundvoltage, namely, a reference voltage GND, an input terminal 23 (33)which serves as a signal input part IN for the high frequency signal,and an output terminal 24 (34) which serves as a signal output part OUTfor the high frequency signal.

The input terminal 23 described above is connected with the outputterminal of the mixer 233 which is shown in FIG. 12, while the outputterminal 14 is connected with an input terminal of the attenuator 244.The resistor 22 plays a role of blocking leakage of the high frequencysignal. Meanwhile, the input terminal 33 is connected with the outputterminal of the mixer 233 which is shown in FIG. 12, and the outputterminal 34 is connected with an input terminal of the attenuator 254.The resistor 32 plays a role of blocking leakage of the high frequencysignal.

FIG. 15 is a drawing which shows voltage control characteristics of theattenuator 244, the attenuator 254, the switch 245 and the switch 255relative to a position to which the mobile telephone terminal device hasmoved. In FIG. 15, the gain control voltages V_(C)(A) and V_(C)(B) andthe switch voltages V_(SW)(A) and V_(SW)(B) are shown.

Operations of the attenuators 244 and 254 and the switches 245 and 255having such structures described above will now be described. The mobiletelephone terminal device is driven at a voltage of up to about 3.0 V bya lithium battery or the like. The threshold voltages of the fieldeffective transistors respectively represent a bias at which thevariable resistors initiate the gain control operation and a bias atwhich the switches initiate the switching operation. The ground voltage(reference voltage) is applied to the gate voltage applying terminal 25(35) of the field effective transistor 21 (31).

In the cell CL(A) which uses the band A, L (0 V) is applied to theswitch voltage applying terminal 26 of the switch 245 to thereby selectthe band A, while H (3.0 V) is applied to the switch voltage applyingterminal 36 of the switch 255 as the band B is not selected. Since thedistance from the base station BS(A) is the shortest within the cellCL(A) when the mobile telephone terminal device is located at the spotdenoted at TH₁, the minimum value (0.5 V) is applied as the gain controlvoltage V_(C)(A) to the gain control voltage applying terminal 5 so thatthe attenuation at the attenuator 244 will become maximum.

In this case, when the mobile telephone terminal device moves from thespot denoted at TH₁ to the spot denoted at TH₀, the gain control voltageV_(C)(A) applied to the gain control voltage applying terminal 5sequentially changes from the minimum value (0.5 V) to the maximum value(2.5 V) to thereby ensure that the attenuation at the attenuator 244will change from the maximum to the minimum.

Simultaneously with the arrival of the mobile telephone terminal deviceat the spot denoted at TH₀, within the cell CL(B) which uses the band B,L (0 V) is applied to the switch voltage applying terminal 36 of theswitch 255 to thereby select the band B and H (3.0 V) is applied to theswitch voltage applying terminal 26 of the switch 245 as the band A isnot selected. In this situation, since a distance between the mobiletelephone terminal device (TH₀) and the base station BS(B) within thecell CL(B) is the longest, the maximum value (2.5 V) is applied as thegain control voltage V_(C)(B) to the gain control voltage applyingterminal 15 so that the attenuation at the attenuator 254 will becomeminimum.

Further, when the mobile telephone terminal device moves from the spotdenoted at TH₀ to the spot denoted at TH₄, the gain control voltageV_(C)(B) applied to the gain control voltage applying terminal 15sequentially changes from the maximum value (2.5 V) to the minimum value(0.5 V) to thereby ensure that the attenuation at the attenuator 254will change from the minimum to the maximum.

Meanwhile, in the variable gain intermediate frequency amplifier 232,the gain control voltage V_(C)(C) is changed independently of selectionof either the band A or B, whereby the output level changescontinuously.

FIG. 16 is a timing chart which shows the timing at which theattenuators shown in FIG. 13 and the switches shown in FIG. 14 operatein response to the switching of the band in accordance with movingbetween the cells. Shown in FIG. 16 are changes of the level P_(OUT)(SW(B)) of the output signal from the switch 255 and the level P_(OUT)(ATT(B)) of the output signal from the attenuator 254.

Problems with the conventional technique will now be described withreference to FIG. 16. When switching from the band A to the band B isattained by means of a combination of the switches 245 and 255 and theattenuators 244 and 254, it takes scores of microseconds until theswitch 255 has stably turned on since application of the switch voltagefor instance as shown in FIG. 16 at the time of the switching of theband, and therefore, the gain control voltage V_(C)(B) is applied to thegain control voltage applying terminal 15 of the attenuator 254 with adelay which is equivalent to this transient response time of the switch255. Hence, differences of the characteristics of the attenuator 254,the variable gain intermediate frequency amplifier 232 and the likecould give rise to a variation in desired gain of the mobile telephoneterminal device immediately after the switching of the band.

FIG. 17 is a drawing for describing the problem above with theconventional technique. FIG. 17 shows changes of the level P_(OUT) ofthe output signal from the antenna in a situation that the mobiletelephone terminal device is communicating under an ideal conditionwhile moving away from the base station at a constant speed.

In relation to the situation described with reference to FIG. 16, such asituation will now be considered that the mobile telephone terminaldevice is communicating under an ideal condition while moving away fromthe base station at a constant speed.

Within the cell CL(B), owing to the gain control function, the levelP_(OUT) of the output signal from the mobile telephone terminal deviceis normally supposed to decrease linearly. However, in the situation asdescribed above, as shown in FIG. 17, the delayed follow-up operationattributed to a delay of feedback control and the discontinuity of theoutput level occurring at the time of the switching of the bandtemporarily pushes out the level P_(OUT) of the output signal of themobile telephone terminal device off from the linear line at the time ofthe switching of the band. As this happens, the intensity of the receivesignal at the base station deviates from the specified value, adifference develops between the levels of the receive signals on theadjacent channels, and the speech therefore gets disturbed or the speechquality deteriorates.

Although the foregoing has described this problem in relation to anexample that the mobile telephone terminal device is moving under anideal condition, actual conditions of moving are much worse, includingsuch a situation that the intensity of the receive signal abruptly dropslow as the mobile telephone terminal device gets behind a building. Theproblem that the intensity of the receive signal at the base stationdeviates from the specified value is thus believed to be rampant, addingto the difficulty of the deteriorated speech quality.

In addition, the control part 110 of the baseband part 100 needs be setup with the three types of the gain control voltages V_(C)(A), V_(C)(B)and V_(C)(C) to control the variable gain high frequency amplifier 241,the variable gain high frequency amplifier 251 and the variable gainintermediate frequency amplifier 232, and further, with the two types ofthe switch voltages V_(SW)(A) and V_(SW)(B), which demands complicatedcontrol for the control part 110.

Further, since the high frequency part 240 and the high frequency part250 respectively require the switch 245 and the switch 255, thecircuitry structure is complex and a large space is necessary. Thisleads to another problem that the mobile telephone terminal device as awhole becomes large.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an attenuator withswitch function which has a simple structure and yet realizes signalswitch control and signal gain control.

Other object of the present invention is to provide a mobile telephoneterminal device which is capable of realizing a high-quality call.

Still other object of the present invention is to provide a mobiletelephone terminal device which simplifies a structure for band switchcontrol and gain control.

Another object of the present invention is to provide a mobile telephoneterminal device which realizes a space-saving compact size.

A first attenuator with switch function according to the presentinvention comprises: a first variable resistor inserted in a firstsignal line which connects a first signal input part with a first signaloutput part; and a second variable resistor inserted in a second signalline which is disposed parallel to the first signal line and connects asecond signal input part with a second signal output part, wherein asthe attenuation of each one of the first and the second variableresistors is controlled by means of a gain control voltage, either oneof outputs on the first and the second signal lines is blocked and thegain of the remaining output on the first and the second signal lines iscontrolled linearly and continuously. The first and the second variableresistors described above are formed by at least one or more fieldeffective transistors which are connected in series, for instance.

This structure uses a series variable resistor which is inserted in thefirst signal line and formed by at least one or more field effectivetransistors for instance and a series variable resistor which isinserted in the second signal line and formed by at least one or morefield effective transistors for instance, and the selected signal lineis switched by controlling the attenuation of each variable resistor,and in substance, the variable resistor on the selected signal linelinearly controls the gain of the signal on the signal line. Hence, witha simple structure, it is possible to select a signal line and controlthe signal gain on the selected signal line.

A second attenuator with switch function according to the presentinvention comprises: a first variable resistor inserted in a firstsignal line which connects a first signal input part with a first signaloutput part; a second variable resistor inserted in a second signal linewhich is disposed parallel to the first signal line and connects asecond signal input part with a second signal output part; a first and asecond reference voltage applying parts which are connected respectivelywith the first and the second variable resistors; and a gain controlvoltage applying part which is connected with each one of the first andthe second variable resistors via a common gain control line. The firstand the second variable resistors described above are formed by at leastone or more field effective transistors which are connected in series,for instance.

This structure uses a series variable resistor which is inserted in thefirst signal line and formed by at least one or more series-connectedfield effective transistors for instance and a series variable resistorwhich is inserted in the second signal line and formed by at least oneor more series-connected field effective transistors for instance, andoperations of the at least two or more series variable resistorsdisposed parallel are shifted by an amount which is equivalent to atleast the gain control (switch) operation range or more, and theoperation ranges of the respective series variable resistors are set soas to correspond to the mutually different gain control voltage ranges.In addition, the gain control voltage range of the series variableresistor connected to the first signal line is substantially continuouswith the gain control voltage range of the series variable resistorconnected to the second signal line, whereby the signal line is switchedand the gain is controlled using only one type of gain control voltage.Hence, a variation of the gain at the time of switching of the selectedsignal line is eliminated and it is possible to perform the gain controloperation in response to the switching of the signal line at anextremely high accuracy.

A structure for shifting the operations of the at least two or moreseries variable resistors disposed parallel by an amount which isequivalent to at least the gain control operation range or more may be astructure in which reference voltages are applied respective to thesource of the field effective transistor which serves as one of theseries variable resistors and the gate of the field effective transistorwhich serves as the other one of the series variable resistors, forexample. Since the gain is controlled and switching is controlled usingonly one type of gain control voltage in such a structure, it ispossible to control the gain at an extremely high accuracy. Further, itis possible to freely change the setting of the gain control operationvoltage.

For instance, the second attenuator with switch function according tothe present invention described above has a structure that the firstvariable resistor has a structure that a first resistor is connected atleast with the gate of a first field effective transistor the secondvariable resistor has a structure that a second resistor is connected atleast with the gate of a second field effective transistor, the gate ofthe first field effective transistor is connected with the gain controlvoltage applying part via the first resistor and the gain control line,the source of the second field effective transistor is connected withthe gain control voltage applying part via the gain control line, thesource of the first field effective transistor is connected with thefirst reference voltage applying part, and the gate of the second fieldeffective transistor is connected with the second reference voltageapplying part via the second resistor.

It is preferable that a voltage applied to the second reference voltageapplying part is lower than a voltage applied to the first referencevoltage applying part.

To be more specific, it is preferable that a voltage applied to thesecond reference voltage applying part is lower, by a value which iscalculated by subtracting a difference between gain control voltageswhich completely turn off the first and the second field effectivetransistors from the sum of the threshold voltage of the first fieldeffective transistor and the threshold voltage of the second fieldeffective transistor, than a voltage applied to the first referencevoltage applying part.

Further, it is preferable that the values of voltages applied to thefirst and the second reference voltage applying parts are set such thatthe gain control voltage range over which the first variable resistorperforms a gain control operation will not overlap with the gain controlvoltage range over which the second variable resistor performs a gaincontrol operation.

Further, it is preferable that the values of voltages applied to thefirst and the second reference voltage applying parts are set such thatthe gain control voltage range over which the second variable resistorperforms a gain control operation will be lower than the gain controlvoltage range over which the first variable resistor performs a gaincontrol operation.

Further, it is preferable that the values of voltages applied to thefirst and the second reference voltage applying parts are set such thata gain control voltage which completely turns off the second fieldeffective transistor will be lower than a gain control voltage whichcompletely turns off the first field effective transistor.

In other example of the structure of the second attenuator with switchfunction according to the present invention described above, the firstvariable resistor has a structure that a first resistor is connected atleast with the gate of a first field effective transistor; the secondvariable resistor has a structure that a second resistor is connected atleast with the gate of a second field effective transistor; the gate ofthe first field effective transistor is connected with the gain controlvoltage applying part via the first resistor and the gain control line;the source of the second field effective transistor is connected withthe gain control voltage applying part via the gain control line; athird resistor is inserted between the source of the first fieldeffective transistor and a portion which is connected with the gate ofthe second field effective transistor via the second resistor; a fourthresistor is inserted between the portion, which is connected with thegate of the second field effective transistor via the second resistor,and a basic potential portion; and the source of the first fieldeffective transistor is connected with the first reference voltageapplying part.

A third attenuator with switch function according to the presentinvention comprises: a series circuit of a first and a second variableresistors which are inserted in at least one first signal line whichconnects a first signal input part with a first signal output part; athird variable resistor inserted in a second signal line which connectsa second signal input part with a second signal output part; and afourth variable resistor inserted in a third signal line which connectsa third signal input part with a third signal output part, wherein asthe attenuation of each one of the first, the second, the third and thefourth variable resistors is controlled by means of a gain controlvoltage, the gain of either one of outputs on the first, the second andthe third signal lines is controlled linearly and continuously and theremaining ones of the first, the second and the third signal lines areblocked. The first, the second, the third and the fourth variableresistors described above are formed by at least one or more fieldeffective transistors which are connected in series, for instance.

Although being different from that of the first attenuator with switchfunction in that there are three or more signal lines on which the gaincan be controlled, this structure is otherwise the same as that of thefirst attenuator with switch function.

A fourth attenuator with switch function according to the presentinvention comprises: a series circuit of a first and a second variableresistors which are inserted in at least one first signal line whichconnects a first signal input part with a first signal output part; athird variable resistor inserted in a second signal line which connectsa second signal input part with a second signal output part; a fourthvariable resistor inserted in a third signal line which connects a thirdsignal input part with a third signal output part; a first, a second, athird and a fourth reference voltage applying parts which are connectedrespectively with the first, the second, the third and the fourthvariable resistors; and a gain control voltage applying part which isconnected with each one of the first, the second, the third and thefourth variable resistors via a common gain control line. The first, thesecond, the third and the fourth variable resistors described above areformed by at least one or more field effective transistors which areconnected in series, for instance.

Although being different from that of the second attenuator with switchfunction in that there are three or more signal lines on which the gaincan be controlled, this structure is otherwise the same as that of thesecond attenuator with switch function.

A first mobile telephone terminal device according to the presentinvention uses the first attenuator with switch function according tothe present invention for the purpose of switching of a selected bandbetween two bands and for the purpose of gain control in the selectedband.

In this structure, the first attenuator with switch function accordingto the present invention is used. In this attenuator with switchfunction, the selected band is switched by controlling the attenuationof each variable resistor, and in substance, the variable resistor onthe selected band linearly controls the sending output. This solves aproblem of a delay due to a transient response time of a switchassociated with switching of the band, prevents a situation that anoutput from the mobile telephone device terminal temporarily deviatesfrom a desired linear line at the time of switching of the band becauseof a delayed follow-up operation caused by delayed feedback control orthe discontinuity of the output level occurring at the time of theswitching of the band, and realizes a high-quality call. Further, sincethis requires merely gain control for switching of the selected band,control for switching of the band is simplified. In addition, thispermits to omit switches for switching of the band in a high frequencypart, saves the space and achieves a small size.

A second mobile telephone terminal device according to the presentinvention uses the second attenuator with switch function according tothe present invention for the purpose of switching of a selected bandbetween two bands and for the purpose of gain control in the selectedband.

In this structure, the second attenuator with switch function accordingto the present invention is used. Operations of the series variableresistors, which are formed by at least two or more field effectivetransistors disposed parallel, are shifted by an amount which isequivalent to at least the gain control (switch) operation range ormore, and the operation ranges of the respective series variableresistors are set so as to correspond to the mutually different gaincontrol voltage ranges. In addition, the gain control voltage range ofthe series variable resistor connected to the first signal line issubstantially continuous with the gain control voltage range of theseries variable resistor connected to the second signal line, wherebythe band is switched and the gain is controlled using only one type ofgain control voltage. Hence, a variation of the gain at the time ofswitching of the selected band is eliminated and it is possible toperform the gain control operation in response to the switching of theband at an extremely high accuracy.

As a result, the mobile telephone terminal device which is fabricatedusing such an attenuator with switch function above solves a problem ofa delay due to a transient response time of a switch associated withswitching of the band, prevents a situation that an output from themobile telephone device terminal temporarily deviates from a desiredlinear line at the time of switching of the band because of a delayedfollow-up operation caused by delayed feedback control or thediscontinuity of the output level occurring at the time of the switchingof the band, and realizes a high-quality call. Further, since thisrequires merely gain control for switching of the selected band, controlfor switching of the band is simplified. In addition, this permits toomit switches for switching of the band, saves the space and achieves asmall size.

A third mobile telephone terminal device according to the presentinvention is characterized in using the third attenuator with switchfunction according to the present invention for the purpose of switchingof a selected band between three or more bands and for the purpose ofgain control in the selected band.

Although being different from that of the first mobile telephoneterminal device in that there are three or more signal lines on whichthe gain can be controlled, this structure is otherwise the same as thatof the first mobile telephone terminal device.

A fourth mobile telephone terminal device according to the presentinvention is characterized in using the fourth attenuator with switchfunction according to the present invention for the purpose of switchingof a selected band between three or more bands and for the purpose ofgain control in the selected band.

Although being different from that of the second mobile telephoneterminal device in that there are three or more signal lines on whichthe gain can be controlled, this structure is otherwise the same as thatof the second mobile telephone terminal device.

A fifth mobile telephone terminal device according to the presentinvention comprises a baseband part, which processes a speech signal anda radio part, which receives the speech signal processed by the basebandpart and communicates with a base station. The radio part is comprisedof a sender part which generates a send signal to the base station and areceiver part which receives the send signal from the base station. Thesender part is comprised of an intermediate frequency part, which isformed by a modulator which modulates an intermediate frequency signalin accordance with the speech signal which is provided from the basebandpart a variable gain intermediate frequency amplifier which controls thegain of the intermediate frequency signal and a mixer which performsmixing for frequency conversion from the intermediate frequency signalinto a high frequency signal, and a high frequency part which amplifiesthe high frequency signal outputted from the intermediate frequency partand supplies to an antenna. The high frequency part is comprised of again controller with switch function, which switches a selected bandbetween two bands outputted from the intermediate frequency part andcontrols the gain of the high frequency signal in the selected band, andtwo power amplifiers which respectively power-amplify two outputs fromthe gain controller with switch function. The gain controller withswitch function includes an attenuator with switch function whichswitches a selected band between two bands outputted from theintermediate frequency part and controls the gain of the high frequencysignal in the selected band.

The baseband part includes a control part. The control part detectssignal information about a receive signal received by the receiver partand adds a gain control voltage corresponding to this information to theattenuator with switch function so that an output from either one of thetwo power amplifiers is taken over by an output from the other one ofthe two power amplifiers; a target value for the output level of theother one of the two power amplifiers is then set in accordance with thesignal information about the receive signal; the output level of theother one of the two power amplifiers is compared with the target valuefor the output level of the other one of the two power amplifiers; again control voltage corresponding to the result of the comparison isadded to the attenuator with switch function and the variable gainintermediate frequency amplifier, thereby follow-up controlling thegains of the attenuator with switch function and the variable gainintermediate frequency amplifier such that the output level of the otherone of the two power amplifiers will become equal to the target valuefor the output level of the other one of the two power amplifiers.

As an attenuator with switch function, the first attenuator with switchfunction according to the present invention is used. This attenuatorwith switch function switches from the output from one power amplifierto the output from another power amplifier, and controls the gain of theoutput from another power amplifier linearly and continuously.

In this attenuator with switch function, the first attenuator withswitch function according to the present invention is used. In thisattenuator with switch function, the selected band is switched bycontrolling the attenuation of each variable resistor, and in substance,the variable resistor on the selected band linearly controls the outputfrom the power amplifier. This solves a problem of a delay due to atransient response time of a switch associated with switching of theband, prevents a situation that an output from the mobile telephonedevice terminal temporarily deviates from a desired linear line at thetime of switching of the band because of a delayed follow-up operationcaused by delayed feedback control or the discontinuity of the outputlevel occurring at the time of the switching of the band, and realizes ahigh-quality call. Further, since this requires merely gain control forswitching of the selected band at the high frequency part, control forswitching of the band is simplified. In addition, this permits to omitswitches for switching of the band in a high frequency part, saves thespace and achieves a small size.

A sixth mobile telephone terminal device according to the presentinvention uses the second attenuator with switch function according tothe present invention as an attenuator with switch function, and isotherwise the same as the fifth mobile telephone terminal device.

In this structure, the second attenuator with switch function accordingto the present invention is used as an attenuator with switch function.Operations of the series variable resistors, which are formed by atleast two or more field effective transistors disposed parallel forinstance, are shifted by an amount which is equivalent to at least thegain control (switch) operation range or more, and the operation rangesof the respective series variable resistors are set so as to correspondto the mutually different gain control voltage ranges. In addition, thegain control voltage range of the series variable resistor connected tothe first signal line is substantially continuous with the gain controlvoltage range of the series variable resistor connected to the secondsignal line, whereby the band is switched and the gain is controlledusing only one type of gain control voltage. Hence, a variation of thegain at the time of switching of the selected band is eliminated and itis possible to perform the gain control operation in response to theswitching of the band at an extremely high accuracy.

As a result, the mobile telephone terminal device which is fabricatedusing such an attenuator with switch function above solves a problem ofa delay due to a transient response time of a switch associated withswitching of the band, prevents a situation that an output from themobile telephone device terminal temporarily deviates from a desiredlinear line at the time of switching of the band because of a delayedfollow-up operation caused by delayed feedback control or thediscontinuity of the output level occurring at the time of the switchingof the band, and realizes a high-quality call. Further, since thisrequires merely gain control for switching of the selected band at thehigh frequency part, control for switching of the band is simplified. Inaddition, this permits to omit switches for switching of the band in ahigh frequency part, saves the space and achieves a small size.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram which shows the structure of a mobiletelephone terminal device according to a first preferred embodiment ofthe present invention;

FIG. 2 is a block diagram which shows the structure of an attenuatorwith switch function disposed within the mobile telephone terminaldevice which is shown in FIG. 1;

FIG. 3 is a circuitry diagram which shows the specific structure of theattenuator with switch function which is shown in FIG. 2;

FIG. 4 is a chart which shows switch and gain control characteristicsrelative to a gain control voltage within the attenuator with switchfunction which is shown in FIG. 3;

FIG. 5 is a characteristic chart which shows the output power of themobile telephone terminal device observed within the attenuator withswitch function which is shown in FIG. 3, relative to a distance from abase station while the mobile telephone terminal device moves betweencells;

FIG. 6 is a circuitry diagram which shows the specific structure of theattenuator with switch function of FIG. 3 as it is modified to comprisebias resistors 57 and 58 so as to apply a reference voltage upon eachvariable resistor;

FIG. 7 is a block diagram which shows the structure of an attenuatorwith switch function according to a second preferred embodiment of thepresent invention;

FIG. 8 is a chart which shows switch and gain control characteristicsrelative to a gain control voltage observed within the attenuator withswitch function which is shown in FIG. 7;

FIG. 9 is a schematic drawing which shows a positional relationshipbetween a base station and a mobile telephone terminal device;

FIG. 10 is an explanatory drawing which shows the intensities of receivesignals within the base station on the respective channels;

FIG. 11 is a schematic drawing which shows a positional relationshipbetween a base station and a mobile telephone terminal device while themobile telephone terminal device moves between cells;

FIG. 12 is a block diagram which shows the structure of a conventionalmobile telephone terminal device;

FIG. 13 is a circuitry diagram which shows the structure of attenuatorsused in the mobile telephone terminal device which is shown in FIG. 12;

FIG. 14 is a circuitry diagram which shows the structure of switchesused in the mobile telephone terminal device which is shown in FIG. 12;

FIG. 15 is a drawing of the set characteristics of the gain controlvoltage and the switch voltage observed within the attenuators shown inFIG. 13 and the switches shown in FIG. 14 while the mobile telephoneterminal device moves between cells;

FIG. 16 is a timing chart which shows the timing at which theattenuators shown in FIG. 13 and the switches shown in FIG. 14 operatein response to the switching of the band in accordance with movingbetween the cells; and

FIG. 17 is an explanatory drawing for describing the problem with theconventional technique.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The first preferred embodiment of the present invention will bedescribed below with reference to FIGS. 1 through 6.

FIG. 1 is a block diagram of a mobile telephone terminal deviceaccording to the first preferred embodiment of the present invention.The structure and operations of the mobile telephone terminal deviceaccording to the first preferred embodiment will now be described withreference to FIG. 1.

This mobile telephone terminal device is comprised of, as shown in FIG.1, a baseband part 101 which is formed by a microcomputer logic part orthe like and processes a speech signal and a radio part 201 whichreceives the speech signal processed by the baseband part 101 andcommunicates with a base station.

The radio part 201 comprises a sender part 260 which generates a sendsignal to the base station and a receiver part 220 which receives a sendsignal from the base station.

The sender part 260 is comprised of an intermediate frequency part 230and a high frequency part 270. The intermediate frequency part 230modulates a speech signal fed from the baseband part 101, adjusts thegain of an intermediate frequency signal and performs mixing forfrequency conversion. The high frequency part 270 amplifies a highfrequency signal outputted from the intermediate frequency part 230 andsupplies to an antenna 300 via a switch 310.

The intermediate frequency part 230 is comprised of a modulator 231which modulates an intermediate frequency signal in accordance with thespeech signal fed from the baseband part 101, a variable gainintermediate frequency amplifier 232 which amplifies, using a variablegain, the intermediate frequency signal which is an output signal fromthe modulator 231, and a mixer 233 which is for converting an outputsignal from the variable gain intermediate frequency amplifier 232 intoa high frequency.

The variable gain intermediate frequency amplifier 232 described aboveis formed by a bipolar transistor in many instances. The variable gainintermediate frequency amplifier 232 is capable of varying the gain overthe range of about 30 dB at the linearity of ±1 dB. In this case, thegain is continuously controlled over the range of about 30 dB, by meansof a gain control voltage which changes continuously.

The high frequency part 270 is comprised of a gain controller withswitch function 271 which switches the selected band for and controlsthe gain of the high frequency signal outputted from the intermediatefrequency part 230, a power amplifier 242 which power-amplifies anoutput in the band A from the gain controller with switch function 271,and a power amplifier 252 which power-amplifies an output in the band Bfrom the gain controller with switch function 271. The gain controllerwith switch function 271 is capable of switching the selection of theband A or B and varying the gain over the range of about 20 dB at thelinearity of ±1 dB in the selected band. In this case, the bandswitching/selecting operation is executed in response to a gain controlvoltage which changes continuously and the gain is continuouslycontrolled over the range of about 20 dB or higher.

The gain controller with switch function 271 is comprised of apreamplifier (intermediate power amplifier) 243 for the band A, apreamplifier (intermediate power amplifier) 253 for the band B, and anattenuator with switch function 272. The attenuator with switch function272 is cascaded with the preamplifier 243 and selects/switches a band-Ahigh frequency signal which is fed to the power amplifier (high poweramplifier) 242 while simultaneously varying the gain. Further, theattenuator with switch function 272 is cascaded with the preamplifier253 and selects/switches a band-B high frequency signal which is fed tothe power amplifier (high power amplifier) 252 while simultaneouslyvarying the gain.

The attenuator with switch function 272, as described above, switchesthe selection of the band A or B and varies the gain over the range ofabout 20 dB at the linearity of ±1 dB in the selected band. To this end,the attenuator with switch function 272 has a switch isolation value of20 dB or higher and is equipped with a function of varying the gain overthe range of about 20 dB or higher as the attenuation of theattenuators.

Although this embodiment requires that power is amplified in the band Athrough the two stages of amplifiers which are the preamplifier 243 andthe power amplifier 242 but amplified in the band B through the twostages of amplifiers which are the preamplifier 253 and the poweramplifier 252, power may be amplified in the bands A and B each throughone stage of amplifier.

The baseband part 101 includes a control part 120 which is formed by amicrocomputer logic part or the like. The control part 120 detects thesignal intensity of the receive signal reaching the receiver part 220.At the same time, in the band A, the control part 120 detects the outputlevel of the power amplifier 242 and sets a target value for the outputlevel of the power amplifier 242 in accordance with the signal intensityof the receive signal. The output level of the power amplifier 242 iscompared with the target value for the output level of the poweramplifier 242, a gain control voltage V_(C)(D) corresponding to thecomparison result is added to the attenuator with switch function 272,while the gain control voltage V_(C)(C) is added to the variable gainintermediate frequency amplifier 232. In this manner, the gain at theattenuator with switch function 272 and the gain at the variable gainintermediate frequency amplifier 232 are follow-up controlled so thatthe output level of the power amplifier 242 will coincide with thetarget value for the output level of the power amplifier 242.

Further, in the band B, the control part 120 detects the output level ofthe power amplifier 252 and sets a target value for the output level ofthe power amplifier 252 in accordance with the signal intensity of thereceive signal. The output level of the power amplifier 252 is comparedwith the target value for the output level of the power amplifier 252,the gain control voltage V_(C)(D) corresponding to the comparison resultis added to the attenuator with switch function 272, while the gaincontrol voltage V_(C)(C) is added to the variable gain intermediatefrequency amplifier 232. In this manner, the gain at the attenuator withswitch function 272 and the gain at the variable gain intermediatefrequency amplifier 232 are follow-up controlled so that the outputlevel of the power amplifier 252 will coincide with the target value forthe output level of the power amplifier 252.

Utilizing both gain control at the gain controller with switch function271 and gain control at the variable gain intermediate frequencyamplifier 232, the mobile telephone terminal device described aboverealizes gain control over the range of 50 dB or higher at the linearityof ±1 dB in the selected band. According to the PDC standard, the inputstage of the mixer 233 operates in the 200 MHz band while the outputstage of the mixer 233 operates in the 940 or 1441 MHz band. It is +30dBm (where 0 dBm=1 mW) at the output terminal of the power amplifier 242or the power amplifier 252, it is +8 dBm at the output terminal of thepreamplifier 243 or the preamplifier 253, it is −16 dBm at the outputterminal of the attenuator with switch function 272, it is −15 dBm atthe output terminal of the mixer 233, and it is −20 dBm at the outputterminal of the variable gain intermediate frequency amplifier 232.

When the gain controller with switch function 271 controls the gain overthe range of 20 dB and the variable gain intermediate frequencyamplifier 232 controls the gain over the range of 30 dB, the signallevel at the output terminal of the variable gain intermediate frequencyamplifier 232 changes in the range of −20 dBm through −50 dBm.Meanwhile, the signal level at the output terminal of the mixer 233changes in the range of −15 dBm through −45 dBm. The signal level at theoutput terminal of the attenuator with switch function 272 changes inthe range of −16 dBm through −36 dBm. The signal level at the outputterminal of the preamplifier 243 or the preamplifier 253 changes in therange of +8 dBm through −42 dBm. The signal level at the output terminalof the power amplifier 242 or the power amplifier 252 changes in therange of +30 dBm through −20 dBm.

The specific structure and operations of the attenuator with switchfunction 272 will now be described with reference to FIGS. 2 through 6.

FIG. 2 is a schematic block diagram which shows the structure of theattenuator with switch function 272 which is formed by a semiconductorintegrated circuit device, and FIG. 3 is a circuitry diagram which showsthe specific structure of the attenuator with switch function 272. Thisattenuator with switch function 272 is integrated on one GaASsemiconductor substrate. Such a structure can be integrated also on asilicon substrate, and particularly in the case of a substrate ofsilicon or silicon-germanium, etc., a microcomputer logic part can alsobe integrated at the same time.

When switching of the selected band and control of the gain is realizedby means of at least one series variable resistor in each band usingsuch an attenuator with switch function 272, during gain control at thetime of the switching of the band, control to a desired gain in ashorter period of time is possible as compared to where a switch and anattenuator are both used. This in consequence makes it possible toswitch the selected band and control the gain simultaneously in eachband alone, without providing a structure combining a switch and anattenuator for each band. When more parallel variable resistors areused, it is possible to achieve excellent gain control at the time ofswitching across more bands (modes).

In the attenuator with switch function 272, as shown in FIGS. 2 and 3, asignal line 47, which connects an input terminal 43 serving as a signalinput part IN(A) for the high frequency signal with an output terminal45 serving as a signal output part OUT(A) for the high frequency signal,is disposed parallel to a signal line 48 which connects an inputterminal 44 serving as a signal input part IN(B) for the high frequencysignal with an output terminal 46 serving as a signal output part OUT(B)for the high frequency signal.

A series variable resistor 41 formed by at least one or more fieldeffective transistors is inserted in the signal line 47. A seriesvariable resistor 42 formed by at least one or more field effectivetransistors is inserted in the signal line 48.

The variable resistor 41 and the variable resistor 42 are connected by again control line 49. In the attenuator with switch function 272,reference voltage applying terminals 51 and 52 which act as referencevoltage applying parts are connected respectively with the variableresistors 41 and 42 and reference voltages V_(ref1) and V_(ref2) are fedrespectively to the reference voltage applying terminals 51 and 52.Further, a gain control voltage applying terminal 50 which acts as again control voltage applying part is connected with each one of thevariable resistors 41 and 42 via the gain control line 49.

The variable resistors 41 and 42 are formed respectively by what areobtained by connecting resistors 54 and 56 with the gates of fieldeffective transistors 53 and 55. The field effective transistor 53 whichforms the variable resistor 41 on the signal line 47 has its drainconnected with the input terminal 43 and its source connected with theoutput terminal 45. Meanwhile, the field effective transistor 55 whichforms the variable resistor 42 on the signal line 48 has its drainconnected with the input terminal 44 and its source connected with theoutput terminal 46.

In addition, the field effective transistor 53 which forms the variableresistor 41 has its gate connected with the gain control voltageapplying terminal 50 via the resistor 54 and the gain control line 49,and the field effective transistor 55 which forms the variable resistor42 has its source connected with the gain control voltage applyingterminal 50 via the gain control line 49.

The reference voltage V_(ref1) is applied from the reference voltageapplying terminal 51 to the source of the field effective transistor 53which forms the variable resistor 41, while the reference voltageV_(ref2) is applied from the reference voltage applying terminal 52 tothe gate of the field effective transistor 55 which forms the variableresistor 42.

To block intrusion of the high frequency signal, a lower limit value anda higher limit value are set for the resistors 54 and 56 described abovein the following manner for instance. First, the lower limit value is 1kΩ. The reason is because but for the isolation of 20 dB or higher, theswitching characteristics and the gain control characteristics will beinfluenced, e.g., intrusion of the high frequency signal and anincreased loss. The set value above ensures the isolation of 20 dB orhigher.

The higher limit value is 100 kΩ. The reason is as follows. When thefield effective transistors carry a gate-leak current of 1 μA forexample, the voltage drop V_(DROP) at the resistors inserted in thegates of the field effective transistors are:V _(DROP)=1×10⁻⁶×100×10³=0.1  (V)where the resistance value of the resistors is 100 kΩ. In other words,if the resistance value exceeds 100 kΩ, the control voltage will deviatebeyond 0.1 V, thereby exerting a measurable influence over the gaincontrol characteristics.

Operations of the attenuator with switch function 272 having such astructure will now be described. The mobile telephone terminal device isdriven at a voltage of up to about 3.0 V by a lithium battery or thelike. The threshold voltages of the field effective transistorsrespectively represent a bias at which the variable resistors initiatethe gain control operation, namely, a bias at which the field effectivetransistors completely turn off (pinch-off). Such field effectivetransistors having the equal threshold voltage V_(th) for instance areused as the field effective transistors which form the variableresistors 41 and 42. In this example, the threshold voltage V_(th) is−0.5 V, for example.

The mutually different reference voltages V_(ref1) and V_(ref2) areapplied respectively to the reference voltage applying terminals 51 and52 of the variable resistors 41 and 42. The different reference voltagesV_(ref1) and V_(ref2) applied to the reference voltage applyingterminals 51 and 52 of the variable resistors 41 and 42 will now bedescribed.

The variable resistors formed by the field effective transistorscompletely turn off (pinch off) when a gate-source voltage V_(GS)becomes smaller than the threshold voltage V_(th) of the field effectivetransistors (V_(GS)≦V_(th)), and shows the maximum resistance value. Thegate-source voltage V_(GS) of each field effective transistor isexpressed as a difference (V_(G)−V_(S)) between a gate voltage V_(G) anda source voltage V_(S), and the resistance value changes depending upona combination of the gain control voltage V_(C)(D) and the referencevoltages V_(ref1) and V_(ref2). Hence, as the set values of thereference voltages V_(ref1) and V_(ref2) are changed, the range of thegain control voltage V_(C)(D), over which the gain is controlled (i.e.,the attenuation is controlled) using the variable resistors, iscontrolled.

As for the gain control voltage V_(C)(D), the range of the gain controlvoltage V_(C)(D) which each one of the variable resistors 41 and 42affects may be set such that the ranges of the linear gain controloperations of the variable resistors 41 and 42 will not overlap insubstance with each other. Although the variable resistor 42 is disposedon the low-voltage side and the variable resistor 41 is disposed on thehigh-voltage side in this example, their ranges may be set freely.

Assume now that the threshold value (pinch-off) voltage of the fieldeffective transistor 53 of the variable resistor 41 is defined asV_(th1), the threshold value (pinch-off) voltage of the field effectivetransistor 55 of the variable resistor 42 is defined as V_(th2), a gaincontrol voltage which completely turns off (pinches off) the fieldeffective transistor 53 of the variable resistor 41 is defined asV_(COFF(A)), and a gain control voltage which completely turns off(pinches off) the field effective transistor 55 of the variable resistor42 is defined as V_(COFF(B)). Since the gate-source voltage V_(GS) ofeach field effective transistor is expressed as the difference(V_(G)−V_(S)) between the gate voltage V_(G) and the source voltageV_(S),V _(th1) =V _(COFF(A)) −V _(ref1)  (1)V _(th2) =V _(COFF(B)) −V _(ref2)  (2)

As one can see from the equations (1) and (2), as the gain controlvoltage increases, the gain control operation of the field effectivetransistor 53 changes from OFF to ON and the gain control operation ofthe field effective transistor 55 changes from ON to OFF. In short, thegain control operations of these field effective transistors 53 and 55change in a complementary manner. This is because the gain controlvoltage is applied to the gate of the field effective transistor 53while the gain control voltage is applied to the source of the fieldeffective transistor 55.

This is expressed as:ΔV=V _(COFF(A)) −V _(COFF(B))  (3)where ΔV denotes a difference between the gain control voltagesV_(COFF(A)) and V_(COFF(B)). It is necessary to set the difference ΔV asa positive value. That is, the gain control voltage V_(COFF(A)) needs beset to a larger value than the gain control voltage V_(COFF(B)).

With these settings, the field effective transistor 55 can execute thegain control operation when the field effective transistor 53 iscompletely OFF, and the field effective transistor 53 can execute thegain control operation when the field effective transistor 55 iscompletely OFF. In other words, when one of the field effectivetransistors 53 and 55 is completely OFF, the other one of the fieldeffective transistors 53 and 55 can execute the gain control operation.Such operations mean that it is possible to carry out the switchingoperation and the gain control operation at the same time.

It is further necessary that the difference ΔV is set to such a valuewhich is not influenced by a variation of the threshold value voltage ofeach field effective transistor during fabrication, a change caused by atemperature change, etc. Considering that variations of the thresholdvalue voltages of the field effective transistors during fabrication areabout ±0.1 V and changes associated with temperature changes are about±0.1 V, the difference ΔV needs be set to a value which is at leastequal to or larger than 0.4 V.

The maximum value of the difference ΔV needs be set about 2.0 V orlower. This is because a value which can be outputted as a gain controlvoltage from the control part of the baseband part is within the rangeof 0 through about 3.0 V. In short, it is necessary to set the gaincontrol voltages V_(COFF(A)) and V_(COFF(B)) within this range, and itis necessary to set this value to about 2.0 V or lower so as to executethe gain control operation without an influence by changes associatedwith temperature changes or the like. This preferred embodiment requiresthat V_(COFF(A))=1.5 V, V_(COFF(B))=1.0 V and ΔV=0.5 V.

Substituting the equation (1) in the equation (3), the following isobtained:V _(COFF(B)) =V _(ref1) +V _(th1) −ΔV  (4)

Further substituting the equation (4) in the equation (2), the followingis obtained:V _(ref2) =V _(ref1) +V _(th1) +V _(th2) −ΔV  (5)

Now, assuming that V_(th1)=V_(th2)=V_(th),V _(ref2) =V _(ref1)+2V_(th) −ΔV  (6)

The equation (5) shows it is necessary that the voltage V_(ref2) appliedto the reference voltage applying part 52 of the field effectivetransistor 55 is set to be lower, by a value which is calculated bysubtracting the difference ΔV between the gain control voltagesV_(COFF(A)) and V_(COFF(B)) which completely turn off the fieldeffective transistors 53 and 55 from the sum of the threshold voltageV_(th1) of the field effective transistor 53 and the threshold voltageV_(th2) of the field effective transistor 55, than the voltage V_(ref1)applied to the reference voltage applying part 51 of the field effectivetransistor 53.

Meanwhile, the equation (6) shows it is necessary that the voltageV_(ref2) applied to the reference voltage applying part 52 of the fieldeffective transistor 55 is set to be a voltage value which is lower, bya value which is calculated by subtracting the difference ΔV between thegain control voltages V_(COFF(A)) and V_(COFF(B)) which completely turnoff the field effective transistors 53 and 55 from double the thresholdvoltage values V_(th) of the field effective transistors 53 and 55, thanthe voltage V_(ref1) applied to the reference voltage applying part 51of the field effective transistor 53.

In this preferred embodiment, since V_(th)=−0.5 V and ΔV=0.5 V,V _(ref2) =V _(ref1)−1.5  (7)Thus, the voltage V_(ref2) needs be set lower by 1.5 V than the voltageV_(ref1). In this preferred embodiment therefore, V_(ref1)=2.0 V andV_(ref2)=0.5 V.

As described above, when switching of the selected band and control ofthe gain in the selected band is to be realized simultaneously, thereference voltage V_(ref1) of the variable resistor 41 and the referencevoltage V_(ref2) of the variable resistor 42 are each appropriately set,so that the ranges of the gain control operations of the variableresistor 41 in the band (A) and the variable resistor 42 in the band (B)become complementary with each other and switching of the selected bandand control of the gain in the selected band can be achieved at the sametime using one gain control voltage.

FIG. 4 is a gain control characteristics chart which shows a change ofthe gain (attenuation) in response to the gain control voltage V_(C)(D)of the attenuator with switch function 272 which is shown in FIG. 3.Operations of the attenuator with switch function 272 shown in FIG. 3will now be described with reference to FIG. 4.

When the threshold voltage values V_(th) of the field effectivetransistors are all −0.5 V, the reference voltage V_(ref1) is set to 2.0V and the reference voltage V_(ref2) is set to 0.5 V.

In the event that a voltage of 0 through 0.7 V is applied to the gaincontrol voltage applying terminal 50 (FIG. 4: the gain control voltagerange (a)), the resistance value RON of the variable resistor 41 (FET53) is maximum and the resistance value R_(ON) of the variable resistor42 (FET 55) is minimum. Hence, on a signal received at the inputterminals 43 and 44, the level P_(OUT)(A) of the output signal at theoutput terminal 45 becomes minimum and the level P_(OUT)(B) of theoutput signal at the output terminal 46 becomes maximum. This is a statein which the band (B) is selected and the band (A) is not selected.

In the event that a voltage exceeding 0.7 V is applied to the gaincontrol voltage applying terminal 50 (FIG. 4: the gain control voltagerange (b)), while the resistance value R_(ON) of the variable resistor41 (FET 53) remains maximum, the resistance value R_(ON) of the variableresistor 42 (FET 55) starts increasing. Hence, while the levelP_(OUT)(A) of the output signal at the output terminal 45 stays minimum,the level P_(OUT)(B) of the output signal at the output terminal 46decreases. The gain control voltage range in which a variable resistorformed by a field effective transistor performs a linear gain controloperation would normally be from about 0.2 to about 0.3 V, andtherefore, until application of a voltage of 1.0 V to the gain controlvoltage applying terminal 50, the gain would decrease about 20 dBlinearly. This is a state in which the band (A) is not selected and thegain is controlled in the band (B) with the band (B) kept selected.

With application of a voltage of 1.0 V to the gain control voltageapplying terminal 50 (FIG. 4: the gain control voltage range (c)), theresistance value R_(ON) of the variable resistor 42 (FET 55) which usedto increase reaches the maximum value and the resistance value R_(ON) ofthe variable resistor 41 (FET 53) remains at the maximum value. Hence,the level P_(OUT)(B) of the output signal at the output terminal 46 andthe level P_(OUT)(A) of the output signal at the output terminal 45 eachbecome minimum. This is a state in which the band (A) is not selectedand the band (B) switches from selected to non-selected.

With application of a voltage of 1.5 V to the gain control voltageapplying terminal 50 (FIG. 4: the gain control voltage range (d)), whilethe resistance value R_(ON) of the variable resistor 42 (FET 55) remainsat maximum, the resistance value R_(ON) of the variable resistor 41 (FET53) which used to be maximum starts decreasing. Hence, while the levelP_(OUT)(B) of the output signal at the output terminal 46 remains at theminimum value, the level P_(OUT)(A) of the output signal at the outputterminal 45 starts increasing. This is a state in which the band (A)switches from non-selected to selected, gain control is started in theband (A), and the band (B) is not selected.

Until application of a voltage of 1.8 V to the gain control voltageapplying terminal 50, the level P_(OUT)(A) of the output signal at theoutput terminal 45 increases about 20 dB linearly. During this, theresistance value R_(ON) of the variable resistor 42 (FET 55) remainsmaximum. Because of this, the level P_(OUT)(B) of the output signal atthe output terminal 46 remains at the minimum value.

With application of a voltage of 1.8 V to the gain control voltageapplying terminal 50 (FIG. 4: the gain control voltage range (e)), theresistance value R_(ON) of the variable resistor 42 (FET 55) remainsmaximum and the resistance value R_(ON) of the variable resistor 41 (FET53) which used to decrease reaches the minimum value. Hence, while thelevel P_(OUT)(B) of the output signal at the output terminal 46 remainsat the minimum value, the level P_(OUT)(A) of the output signal at theoutput terminal 45 becomes maximum. This is a state in which the band(A) is selected, the gain is controlled in the band (A), and the band(B) is not selected.

Even with application of a voltage of 1.8 V or higher to the gaincontrol voltage applying terminal 50, the resistance value R_(ON) of thevariable resistor 41 (FET 53) stays at the minimum value and theresistance value R_(ON) of the variable resistor 42 (FET 55) remains atthe maximum value. Hence, the level P_(OUT)(B) of the output signal atthe output terminal 46 remains minimum and the level P_(OUT)(A) of theoutput signal at the output terminal 45 remains maximum.

FIG. 4 also shows the level P_(OUT)(ANT) of the output from the antenna300.

As described above, using the structure that the variable resistors 41and 42 formed by field effective transistors are connected parallel forthe attenuators with switch function, this preferred embodiment ensuresthat each gain control operation range gets shifted thus avoidingoverlapping of the gain control operation ranges of the variableresistors 41 and 42 with each other and hence that the gain controloperations of the variable resistors 41 and 42 become complementary witheach other. This makes it possible to realize switching of the selectedband and control of the gain in the selected band at the same time inresponse to the control voltage. With the reference voltages adjusted byan external microcomputer, the gain control operation ranges of thevariable resistors 41 and 42 are shifted.

Thus, at the high frequency part of the mobile telephone terminaldevice, using one semiconductor device, switching of the selected bandand control of the gain in the selected band is realized. This allows toavoid a temporary deviation from the target values for the output levelsof the power amplifiers which would otherwise occur upon switching ofthe band according to the conventional technique as shown in FIG. 17,and makes it easy as shown in FIG. 5 to highly accurately control thegain while the mobile telephone terminal device switches between thebands.

In addition, since only one type of gain control voltage setup isneeded, it is possible to simplify the circuitry structure of thecontrol part 120. It is also possible to omit the switches in the highfrequency part, save the space and further reduce the size of the mobiletelephone terminal device.

Further, although the reference voltage applying terminal 51 of thevariable resistor 41 which is for the band (A) is separate from thereference voltage applying terminal 52 of the variable resistor 42 whichis for the band (B) in the preferred embodiment described above, astructure as that shown in FIG. 6 may be used instead. That is, only thereference voltage applying terminal 51 may be disposed, thereby dividingthe reference voltage V_(ref1), which is applied to the variableresistor 41, across the bias resistors 57 and 58 and accordinglyapplying a reference voltage to the variable resistor 42. In this case,the circuit is simplified as only one reference voltage applyingterminal is used. The bias resistors 57 and 58 each play a role ofblocking intrusion of the high frequency signal. To prevent intrusion ofthe high frequency signal, the bias resistors 57 and 58 described aboveare set to a resistance value which is from about 5 kΩ to about 100 kΩ.

The reason of setting the bias resistors 57 and 58 to a resistance valuewhich is from about 5 kΩ to about 100 kΩ will now be described.

First, the reason why the lower limit value is about 5 kΩ is as follows.The high frequency signal will be passed on to the ground (GND) andneither the switching operation nor the gain control operation ispossible if the bias resistors 57 and 58 have small values, andtherefore, the bias resistors 57 and 58 need be 5 kΩ or larger(isolation of 40 dB or higher). On the other hand, when the referencevoltage V_(ref1) is 3 V, a current carried by the bias resistors 57 and58 is:I=3 V/10 kΩ=300 μAor larger, thereby pushing up the power consumption.

Meanwhile, the reason why the lower limit value is 100 kΩ is as follows.When the reference voltage V_(ref1) is 3 V, a current carried by thebias resistors 57 and 58 is:I=3 V/200 kΩ=15 μANow, a voltage across the bias resistor 57 is:V=15 μA×100 kΩ=1.5 VAt this stage, a leak current of 1 μA flowing through the fieldeffective transistors would give rise to a bias variation of 1 μA×100kΩ=0.1 V, thereby deviating the gain control characteristics andpreventing accurate gain control.

Although the preferred embodiment described above requires the structurethat the two variable resistors are disposed parallel, i.e., thevariable resistor 41 which is for the band (A) and the variable resistor42 which is for the band (B) both formed by field effective transistors,more variable resistors may be disposed parallel. The larger the numberof the variable resistors disposed parallel is, the larger the number ofthe bands over which switching of the selected band and gain control canbe realized is.

An example of an attenuator with switch function capable of controllingthe gain over three bands will now be described with reference to FIGS.7 and 8.

In this attenuator with switch function, as shown in FIG. 7, a signalline 71, which connects an input terminal 65 serving as a signal inputpart IN (A) for the high frequency signal with an output terminal 68serving as a signal output part OUT(A) for the high frequency signal, asignal line 72, which connects an input terminal 66 serving as a signalinput part IN(B) for the high frequency signal with an output terminal69 serving as a signal output part OUT(B) for the high frequency signal,and a signal line 73, which connects an input terminal 67 serving as asignal input part IN(C) for the high frequency signal with an outputterminal 70 serving as a signal output part OUT(C) for the highfrequency signal, are disposed parallel to each other.

Series variable resistors 61 and 62 formed by at least one or more fieldeffective transistors are inserted in the signal line 71. A seriesvariable resistor 63 formed by at least one or more field effectivetransistors is inserted in the signal line 72. A series variableresistor 64 formed by at least one or more field effective transistorsis inserted in the signal line 73.

The variable resistor 61, the variable resistor 62, the variableresistor 63 and the variable resistor 64 are connected by a gain controlline 74. In this attenuator with switch function, reference voltageapplying terminals 76, 77, 78 and 79 which act as reference voltageapplying parts are connected respectively with the variable resistors61, 62, 63 and 64 and reference voltages V_(ref11), V_(ref12), V_(ref13)and V_(ref14) are fed respectively to the reference voltage applyingterminals 76, 77, 78 and 79. Further, a gain control voltage applyingterminal 75 which acts as a gain control voltage applying part isconnected with each one of the variable resistors 61, 62, 63 and 64 viathe gain control line 74.

The variable resistors 61, 62, 63 and 64 above are formed respectivelyby what are obtained by connecting resistors with the gates of at leastfield effective transistors, like those which are shown in FIG. 3.

The field effective transistor (not shown) which forms the variableresistor 61 has its drain connected with the input terminal 65 and itssource connected with the drain of the field effective transistor (notshown) which forms the variable resistor 62. The field effectivetransistor which forms the variable resistor 62 has its source connectedwith the output terminal 68. The field effective transistor (not shown)which forms the variable resistor 63 has its drain connected with theinput terminal 66 and its source connected with the output terminal 69.The field effective transistor (not shown) which forms the variableresistor 64 has its drain connected with the input terminal 67 and itssource connected with the output terminal 70.

Further, the field effective transistor which forms the variableresistor 61 has its gate connected with the gain control voltageapplying terminal 75 via the resistor and the gain control line 74. Thefield effective transistor which forms the variable resistor 62 has itssource connected with the gain control voltage applying terminal 75 viathe gain control line 74. The field effective transistor which forms thevariable resistor 63 has its source connected with the gain controlvoltage applying terminal 75 via the gain control line 74. The fieldeffective transistor which forms the variable resistor 64 has its gateconnected with the gain control voltage applying terminal 75 via theresistor and the gain control line 74.

The reference voltage V_(ref11) is applied from the reference voltageapplying terminal 76 to the source of the field effective transistorwhich forms the variable resistor 61. The reference voltage V_(ref12) isapplied from the reference voltage applying terminal 77 to the gate ofthe field effective transistor which forms the variable resistor 62 viathe resistor. The reference voltage V_(ref13) is applied from thereference voltage applying terminal 78 to the gate of the fieldeffective transistor which forms the variable resistor 63 via theresistor. The reference voltage V_(ref14) is applied from the referencevoltage applying terminal 79 to the source of the field effectivetransistor which forms the variable resistor 64.

FIG. 8 is a gain control characteristics chart which shows a change ofthe gain (attenuation) in response to the gain control voltage V_(C)(D)of the attenuator with switch function which is shown in FIG. 7.Operations of the attenuator with switch function shown in FIG. 7 willnow be described with reference to FIG. 8.

When the threshold voltage values V_(th) of the field effectivetransistors are all −0.5 V, the reference voltage V_(ref11) is set to1.8 V, the reference voltage V_(ref12) is set to 1.7 V, the referencevoltage V_(ref13) is set to 0.5 V, and the reference voltage V_(ref14)is set to 3.0 V.

In the event that a voltage of 0 through 0.7 V is applied to the gaincontrol voltage applying terminal 75 (FIG. 8: the gain control voltagerange (a)), the resistance values R_(ON) of the variable resistors 61and 64 reach the maximum value and the resistance values R_(ON) of thevariable resistors 62 and 63 reach the minimum value. Hence, on a signalreceived at the input terminals 65, 66 and 67, the level P_(OUT)(A) ofthe output signal at the output terminal 68 becomes minimum, the levelP_(OUT)(B) of the output signal at the output terminal 69 becomesmaximum, and the level P_(OUT)(C) of the output signal at the outputterminal 70 becomes minimum. This is a state in which the band (B) isselected but the bands (A) and (C) are not selected.

In the event that a voltage exceeding 0.7 V is applied to the gaincontrol voltage applying terminal 75 (FIG. 8: the gain control voltagerange (b)), the resistance values R_(ON) of the variable resistors 61and 64 reach the maximum value, the resistance value R_(ON) of thevariable resistor 62 remains at the minimum value, and the resistancevalue R_(ON) of the variable resistor 63 starts increasing. Hence, whilethe level P_(OUT)(A) of the output signal at the output terminal 68remains minimum, the level P_(OUT)(C) of the output signal at the outputterminal 70 remains minimum, and the level P_(OUT)(B) of the outputsignal at the output terminal 69 decreases. The gain control voltagerange in which a variable resistor formed by a field effectivetransistor performs a linear gain control operation would normally befrom about 0.2 to about 0.3 V, and therefore, until application of avoltage of 1.0 V to the gain control voltage applying terminal 75, thegain would decrease about 20 dB linearly. This is a state in which thebands (A) and (C) are not selected and the gain is controlled in theband (B) with the band (B) kept selected.

With application of a voltage of 1.0 V to the gain control voltageapplying terminal 75 (FIG. 8: the gain control voltage range (c)), theresistance value R_(ON) of the variable resistor 63 which used toincrease reaches maximum, while the resistance value R_(ON) of thevariable resistor 62 remains minimum and the resistance values R_(ON) ofthe variable resistors 61 and 64 stay maximum. Hence, the levelP_(OUT)(B) of the output signal at the output terminal 69, the levelP_(OUT)(A) of the output signal at the output terminal 68 and the levelP_(OUT)(C) of the output signal at the output terminal 70 each becomeminimum. This is a state in which the bands (A) and (C) are non-selectedand the band (B) switches from selected to non-selected.

With application of a voltage of 1.3 V to the gain control voltageapplying terminal 75 (FIG. 8: the gain control voltage range (d)), theresistance values R_(ON) of the variable resistors 63 and 64 remainmaximum, the resistance value R_(ON) of the variable resistor 62 remainsminimum and the resistance value R_(ON) of the variable resistor 61which used to be maximum starts decreasing. Hence, while the levelsP_(OUT)(B) and P_(OUT)(C) of the output signals at the output terminals69 and 70 remain at the minimum value, the level P_(OUT)(A) of theoutput signal at the output terminal 68 starts increasing. This is astate in which the band (A) switches from non-selected to selected, gaincontrol is started in the band (A), and the bands (B) and (C) are notselected.

Until application of a voltage of 1.6 V to the gain control voltageapplying terminal 75, the level P_(OUT)(A) of the output signal at theoutput terminal 68 increases about 20 dB linearly. During this, theresistance values R_(ON) of the variable resistors 63 and 64 remain atmaximum, and the levels P_(OUT)(B) and P_(OUT)(C) of the output signalsat the output terminals 69 and 70 remain at the minimum value.

With application of a voltage of 1.6 V to the gain control voltageapplying terminal 75 (FIG. 8: the gain control voltage range (e)), theresistance values R_(ON) of the variable resistors 63 and 64 reachmaximum, the resistance value R_(ON) of the variable resistor 62 remainsminimum and the resistance value R_(ON) of the variable resistor 61which used to decrease reaches the minimum value. Hence, the levelsP_(OUT)(B) and P_(OUT)(C) of the output signals at the output terminals69 and 70 remain at the minimum value, and the level P_(OUT)(A) of theoutput signal at the output terminal 68 becomes maximum. This is a statein which the band (A) is selected, the gain is controlled in the band(A), and the bands (B) and (C) are not selected.

With application of a voltage beyond 1.9 V to the gain control voltageapplying terminal 75 (FIG. 8: the gain control voltage range (f)), theresistance values R_(ON) of the variable resistors 63 and 64 reachmaximum, the resistance value R_(ON) of the variable resistor 61 remainsminimum, but the resistance value R_(ON) of the variable resistor 62starts increasing. Hence, while the levels P_(OUT)(B) and P_(OUT)(C) ofthe output signals at the output terminals 69 and 70 remain minimum, thelevel P_(OUT)(A) of the output signal at the output terminal 68decreases. Until application of a voltage of 2.2 V to the gain controlvoltage applying terminal 75, the gain decreases about 20 dB linearly.This is a state in which the bands (B) and (C) are not selected and thegain is controlled in the band (A) with the band (A) kept selected.

With application of a voltage of 2.2 V to the gain control voltageapplying terminal 75 (FIG. 8: the gain control voltage range (g)), theresistance value R_(ON) of the variable resistor 62 which used toincrease reaches the maximum value, the resistance values R_(ON) of thevariable resistors 63 and 64 become maximum, and the resistance valueR_(ON) of the variable resistor 61 remains minimum. Hence, the levelP_(OUT)(A) of the output signal at the output terminal 68, the levelP_(OUT)(B) of the output signal at the output terminal 69 and the levelP_(OUT)(C) of the output signal at the output terminal 70 each becomeminimum. This is a state in which the bands (B) and (C) are not selectedand the band (A) switches from selected to non-selected.

With application of a voltage of 2.5 V to the gain control voltageapplying terminal 75 (FIG. 8: the gain control voltage range (h)), theresistance values R_(ON) of the variable resistors 62 and 63 reachmaximum, the resistance value R_(ON) of the variable resistor 61 remainsminimum, and the resistance value R_(ON) of the variable resistor 64which used to be maximum starts decreasing. Hence, while the levelsP_(OUT)(A) and P_(OUT)(B) of the output signals at the output terminals68 and 69 remain at the minimum value, the level P_(OUT)(C) of theoutput signal at the output terminal 70 starts increasing. This is astate in which the band (C) switches from non-selected to selected, gaincontrol is started in the band (C), and the bands (A) and (B) are notselected.

Until application of a voltage of 2.8 V to the gain control voltageapplying terminal 75, the level P_(OUT)(C) of the output signal at theoutput terminal 70 increases about 20 dB linearly. During this, theresistance values R_(ON) of the variable resistors 62 and 63 remain atmaximum, the resistance value R_(ON) of the variable resistor 61 remainsminimum, and the levels P_(OUT)(A) and P_(OUT)(B) of the output signalsat the output terminals 68 and 69 remain at the minimum value.

With application of a voltage of 2.8 V to the gain control voltageapplying terminal 75 (FIG. 8: the gain control voltage range (i)), theresistance values R_(ON) of the variable resistors 62 and 63 reachmaximum, the resistance value R_(ON) of the variable resistor 61 remainsminimum, and the resistance value R_(ON) of the variable resistor 64which used to decrease becomes minimum. Hence, while the levelsP_(OUT)(A) and P_(OUT)(B) of the output signals at the output terminals68 and 69 remain at the minimum value, the level P_(OUT)(C) of theoutput signal at the output terminal 70 reaches maximum. This is a statein which the band (C) is selected, the gain is controlled in the band(C), and the bands (A) and (B) are not selected.

Even with application of a voltage of 2.8 V or higher to the gaincontrol voltage applying terminal 75, the resistance values R_(ON) ofthe variable resistors 61 and 64 stay minimum and the resistance valuesR_(ON) of the variable resistors 62 and 63 stay maximum. Hence, whilethe levels P_(OUT)(A) and P_(OUT)(B) of the output signals at the outputterminals 68 and 69 remain minimum, the level P_(OUT)(C) of the outputsignal at the output terminal 70 remains maximum.

A mobile telephone terminal device which uses the attenuator with switchfunction described above is of the type which switches over three bands.

Further, nothing is connected in parallel between the drain and thesource electrodes of the field effective transistors 53 and 55 whichform the respective variable resistors 41 and 42 in the preferredembodiment described above. However, for the purpose of suppressingvariations of the resistance values unique to the respective fieldeffective transistors 53 and 55 and controlling the variable resistanceranges, resistors or the like may be connected parallel between thedrain and the source electrodes of the field effective transistors 53and 55. This stabilizes the amount of gain control at each variableresistor and realizes gain control at an extremely high accuracy.

Further, although the preferred embodiment described above demands thata field effective transistor having one gate is used as each one of thefield effective transistors 53 and 55 which respectively form therespective variable resistors 41 and 42, a field effective transistorhaving two or more gates (of the multiple-gate type) may be usedinstead. The more gates a field effective transistor has, the wider thegain control width becomes, and in addition, even use of a high inputsignal achieves switch control and gain control accompanying only asuppressed deterioration of distortion characteristics. Further, whilethe foregoing has described that one field effective transistor is usedfor each one of the variable resistors 41 and 42, each variable resistormay be formed by a series circuit of two or more field effectivetransistors.

Further, while the preferred embodiment described above is directed toan example that the field effective transistors 53 and 55 are used torespectively form the variable resistors 41 and 42, the presentinvention is not limited to this. Elements such as diodes may be usedfor instance.

These attenuators can be used not only for the PDC method but forvarious mobile telecommunications methods (CDMA (IS-95), GSM, PCS, DCS,Wideband-CDMA, CDMA2000, PHS, etc.).

1. An attenuator with switch function, comprising: a first variableresistor inserted in a first signal line which connects a first signalinput part with a first signal output part; a second variable resistorinserted in a second signal line which is disposed parallel to saidfirst signal line and connects a second signal input part with a secondsignal output part; a first and a second reference voltage applyingparts which are connected respectively with said first and said secondvariable resistors and are applied respectively with different referencevoltages; and a gain control voltage applying part which is connectedwith each one of said first and said second variable resistors via acommon gain control line, wherein as the attenuation of each one of saidfirst and second variable resistors is controlled via said gain controlvoltage, either one of outputs on said first and second signal lines isblocked and the gain of the remaining output on said first and secondsignal lines is controlled linearly and continuously.
 2. The attenuatorwith switch function of claim 1, wherein said first variable resistorhas a structure that a first resistor is connected at least with thegate of a first field effective transistor, said second variableresistor has a structure that a second resistor is connected at leastwith the gate of a second field effective transistor, the gate of saidfirst field effective transistor is connected with said gain controlvoltage applying part via said first resistor and said gain controlline, the source of said second field effective transistor is connectedwith said gain control voltage applying part via said gain control line,the source of said first field effective transistor is connected withsaid first reference voltage applying part, and the gate of said secondfield effective transistor is connected with said second referencevoltage applying part via said second resistor.
 3. The attenuator withswitch function of claim 2, wherein a voltage applied to said secondreference voltage applying part is lower, by a value which is calculatedby subtracting a difference between gain control voltages whichcompletely turn off said first and said second field effectivetransistors from the sum of the threshold voltage of said first fieldeffective transistor and the threshold voltage of said second fieldeffective transistor, than a voltage applied to said first referencevoltage applying part.
 4. The attenuator with switch function of claim2, wherein the values of voltages applied to said first and said secondreference voltage applying parts are set such that a gain controlvoltage which completely turns off said second field effectivetransistor will be lower than a gain control voltage which completelyturns off said first field effective transistor.
 5. The attenuator withswitch function of claim 2, wherein the values of voltages applied tosaid first and said second reference voltage applying parts are set suchthat only when one of said first and said second field effectivetransistors is completely off, the other one of said first and saidsecond field effective transistors will perform a gain controloperation.
 6. The attenuator with switch function of claim 1, wherein avoltage applied to said second reference voltage applying part is lowerthan a voltage applied to said first reference voltage applying part. 7.The attenuator with switch function of claim 1, wherein the values ofvoltages applied to said first and said second reference voltageapplying parts are set such that the gain control voltage range overwhich said first variable resistor performs a gain control operationwill not overlap with the gain control voltage range over which saidsecond variable resistor performs a gain control operation.
 8. Theattenuator with switch function of claim 1, wherein the values ofvoltages applied to said first and said second reference voltageapplying parts are set such that the gain control voltage range overwhich said second variable resistor performs a gain control operationwill be lower than the gain control voltage range over which said firstvariable resistor performs a gain control operation.
 9. The attenuatorwith switch function of claim 1, wherein said first variable resistorhas a structure that a first resistor is connected at least with thegate of a first field effective transistor; said second variableresistor has a structure that a second resistor is connected at leastwith the gate of a second field effective transistor; the gate of saidfirst field effective transistor is connected with said gain controlvoltage applying part via said first resistor and said gain controlline; the source of said second field effective transistor is connectedwith said gain control voltage applying part via said gain control line;a third resistor is inserted between the source of said first fieldeffective transistor and a portion which is connected with the gate ofsaid second field effective transistor via said second resistor; afourth resistor is inserted between said portion, which is connectedwith the gate of said second field effective transistor via said secondresistor, and a basic potential portion; and the source of said firstfield effective transistor is connected with said first referencevoltage applying part.
 10. An attenuator with switch function,comprising: a series circuit of a first and a second variable resistorswhich are inserted in at least one first signal line which connects afirst signal input part with a first signal output part; and a thirdvariable resistor inserted in a second signal line which is disposedparallel to said first signal line and connects a second signal inputpart with a second signal output part; a fourth variable resistorinserted in a third signal line which connects a third signal input partwith a third signal output part, wherein as the attenuation of each oneof said first, said second, said third and said fourth variableresistors is controlled by means of a gain control voltage, the gain ofeither one of outputs on said first, said second and said third signallines is controlled linearly and continuously and the remaining ones ofsaid first, said second and said third signal lines are blocked.
 11. Anattenuator with switch function, comprising: a series circuit of a firstand a second variable resistors which are inserted in at least one firstsignal line which connects a first signal input part with a first signaloutput part; a third variable resistor inserted in a second signal linewhich connects a second signal input part with a second signal outputpart; a fourth variable resistor inserted in a third signal line whichconnects a third signal input part with a third signal output part; afirst, a second, a third and a fourth reference voltage applying partswhich are connected respectively with said first, said second, saidthird and said fourth variable resistors and are applied respectivelywith different reference voltages; and a gain control voltage applyingpart which is connected with each one of said first, said second, saidthird and said fourth variable resistors via a common gain control line.